1. Field of the Invention
The present invention relates to a radio frequency front-end circuit including a multiplexer, and also relates to a communication device.
2. Description of the Related Art
Recently, communication devices, for example, cellular phones, have been desired to operate in a multiband mode in which the device is adaptable for a plurality of frequency bands (also simply called “bands”) with one terminal. According to this a trend, radio frequency front-end circuits, for example, front-end modules, incorporated in the communication devices have also been desired to operate in the multiband mode. Such a radio frequency front-end circuit has been further desired to be adaptable for the so-called CA (carrier aggregation) in which radio frequency signals in multiple bands are transmitted and/or received at the same time or substantially the same time.
As one example of the above-mentioned radio frequency front-end circuit, a diversity module including a diplexer, a switch IC (Integrated Circuit), a plurality of BPF's (Bandpass Filters), and an LNA (Low Noise Amplifier), which are connected successively in the named order, is disclosed (see, e.g., U.S. Patent Application Publication No. 2016/0127015). The disclosed radio frequency front-end circuit is adaptable for the CA because two or more of the plurality of BPF's are selected by the switch IC.
With the related-art described above, however, when radio frequency signals in multiple bands are transmitted and/or received at the same time or substantially the same time as in the CA, the radio frequency signal in one band not only passes through a filter including a pass band corresponding to the relevant one band, but also leaks to another filter. Thus, looking at the other filter, the radio frequency signal in the band outside its own pass band leaks into the other filter, and an attenuation in the band outside the pass band of the other filter is reduced. This leads to degradation of attenuation characteristics in the other filter. Furthermore, in the one filter, the radio frequency signal in its pass band leaks out therefrom, and a loss in the relevant pass band increases. This leads to degradation of bandpass characteristics. As a result, the related-art has the problem that it is difficult to satisfactorily ensure the attenuation characteristics and the bandpass characteristics of the radio frequency front-end circuit in an overall range.